But this is literally the entire point of the this paper. The sentence you just pasted was the the previous state of the art, this paper makes the point that they have now imaged them in cells (using i-motif specific antibodies).
Edit: For clarity - all the in cell work is cultured cell lines and not cells taken from an animal model or in situ imaging.
Literally my only point was that 'this might not matter for biology because we've not even seen it in cells' is no longer true. It still might not matter for biology though!